1. Field of the Invention
The present invention relates to a frequency converter used for a receiver which receives signals in a UHF band or signals in a microwave band, and particularly to a frequency converter which is capable of easily attenuating interference signals generated by image signals.
2. Prior Art
Frequency converters have been known which are capable of attenuating image signals without using a narrow band-pass filter in a receiver which receives signals of a UHF band or signals of a microwave band, as disclosed in Japanese Patent Laid-Open Nos. 75709/1981 and 193106/1982.
These frequency converters usually have a plurality of signal dividers or hybrid couplers to generate two signals with phases that are different by 90 degrees, and two image signals with phases that are different by 180 degrees, so that the image signals are cancelled when the frequency of the main signals that are being received is converted. That is, interference signals generated by the image signals are removed.
In general, a signal divider used for the above-mentioned frequency converters is constituted by microstrip lines, and is not suited for obtaining two signals with a phase difference of 90 degrees over a wide frequency range, and is not hence capable of sufficiently attenuating interference signals generated by image signals for the input signals of a wide frequency region.